@article{fdi:010073776,
  title = {{R}everse dichromatism in gem andalusite related to total pleochroism of the {F}e2+-{T}i4+ {IVCT}},
  author = {{R}ondeau, {B}. and {C}hamard-{B}ois, {S}. and {F}ritsch, {E}mmanuel and {N}otari, {F}. and {C}hauvire, {B}.},
  editor = {},
  language = {{ENG}},
  abstract = {{W}e document a dichromatism effect in gem andalusite that shifts from light brownish pink at low thickness to medium green at high thickness. {T}his is roughly reverse to that usually observed in other dichromatic materials. {W}e show that this is due to a very strong pleochroism in andalusite, when dichromatism in other materials is due to an alexandrite effect. {H}ere, colors varies from a strongly absorbing orangey-brown in the c direction to much less absorbing medium green in a and b directions. {T}he brown absorption is so strong that it becomes opaque (total absorption) for thickness above about 1.5 mm (this value may vary according to concentration of the chromophore and intensity of the light source), and hence does not contribute to coloration anymore. {F}or such high thicknesses, only the a and b directions remain transparent and hence only the green component contributes to the color: the sample appears green. {F}or lower thicknesses, the green color combines with the orangey-brown color that becomes transparent along the c direction, resulting in a light brownish pink. {F}rom trace elements analysis in zoned samples, we also confirm that the dark orangey-brown color is due to {F}e2+-{T}i4+, and bring evidences that the light green color is mostly due to {F}e, either in the form of isolated {F}e3+ or {F}e2+-{F}e3+ {IVCT}, with possibly some contributions from isolated {M}n3+.},
  keywords = {{A}ndalusite ; {R}everse dichromatism ; {T}otal absorption ; {P}leochroism},
  booktitle = {},
  journal = {{S}pectrochimica {A}cta {P}art a : {M}olecular and {B}iomolecular {S}pectroscopy},
  volume = {204},
  numero = {},
  pages = {611--619},
  ISSN = {1386-1425},
  year = {2018},
  DOI = {10.1016/j.saa.2018.06.053},
  URL = {https://www.documentation.ird.fr/hor/fdi:010073776},
}